1. Field of the Invention
The invention pertains to the field of urethane catalysts and is more particularly related to catalyst systems employing morpholine and piperazine derivatives in a homogeneous activator solution.
2. Description of Related Art
The use of a catalyst in preparing polyurethanes by the reaction of a polyisocyanate, a polyol and perhaps other ingredients is known. The catalyst is employed to promote at least two, and sometimes three major reactions that must proceed simultaneously and competitively at balanced rates during the process in order to provide polyurethanes with the desired physical characteristics. One reaction is a chain-extending isocyanate-hydroxyl reaction by which a hydroxyl-containing molecule is reacted with an isocyanate-containing molecule to form a urethane. This increases the viscosity of the mixture and provides a polyurethane containing secondary nitrogen atoms in the urethane groups. A second reaction is a crosslinking isocyanate urethane reaction by which an isocyanate-containing molecule reacts with a urethane group containing a secondary nitrogen atom. The third reaction which may be involved is an isocyanate-water reaction by which an isocyanate-terminated molecule is extended and by which carbon dioxide is generated to blow or assist in the blowing of foam. This third reaction is not essential if an extraneous blowing agent, such as a halogenated, normally liquid hydrocarbon, carbon dioxide, etc., is employed, but is essential if all or even part of the gas for foam generation is to be generated by this in-situ reaction (e.g., in the preparation of "one-shot" flexible polyurethane foams).
The reactions must proceed simultaneously at optimum balanced rates relative to each other in order to obtain a good foam structure. If carbon dioxide evolution is too rapid in comparison with chain extension, the foam will collapse. If the chain extension is too rapid in comparison with carbon dioxide evolution, foam rise will be restricted, resulting in a high density foam with a high percentage of poorly defined cells. The foam will not be stable in the absence of adequate crosslinking.
It has long been known that tertiary amines are effective for catalyzing the second crosslinking reaction. Typical amines of this type are found in U.S. Pat. Nos. 4,012,445; 3,925,268; 3,786,005; 4,011,223; 4,048,107; 4,038,210, 4,033,911; 4,026,840; 4,022,720 and 3,912,689. However, many amines of this class have a strong amine odor which is carried over to the polyurethane foam.
Aminoamides may also be used as urethane catalysts such as the N,N-bis(3-dimethylaminopropyl)acetamide of U.S. Pat. No. 3,234,153. Morpholine derivatives as urethane catalysts are described in U.S. Pat. No. 3,645,925 which discloses 4,4'-dimorpholinodiethylether and U.S. Pat. No. 4,228,248 which uses certain N-alkoxyalkyl morpholines. A method for making N-alkylmorpholines, from which some of the previously described catalysts may be made, is described in U.S. Pat. No. 3,087,928.
In still other cases, some tertiary amines impart a color to the product foam known as "pinking" and/or cause or fail to prevent undue foam shrinkage. For example, N-methoxypropylmorpholine is an amine catalyst which will produce a pink foam.
In addition to problems of odor, pinking, etc., other tertiary amines suffer still further deficiencies. For example, in some instances the compounds are relatively high in volatility leading to obvious safety problems. In addition, some catalysts of this type do not provide sufficient delay in foaming, which delay is particularly desirable in molding applications to allow sufficient time to situate the preform mix in the mold. Yet other catalysts, while meeting specifications in this area, do not yield foams with a desirable tack-free time. In addition, some catalysts of this type are solids causing handling problems. In many cases, blends of catalysts containing different tertiary amine groups must be utilized in order to achieve the desired balance between gelling and flowing of foams. Lastly, some catalysts of this type cannot be used to form the desired polyurethane foam, such as a low-density foam, say of the polyester type.
The manufacture of polyester urethane foams frequently employs an activator solution which is a blend of the catalyst, surfactant and water to be used in making the foam. The use of an activator solution reduces the number of streams that must match up at the mixing head thereby cutting down on mixing adjustment problems. However, if an activator solution is used it must be homogeneous; that is, it must not separate into different phases, to function properly in the foam formulation. If a homogeneous activator solution is used, it must have a low viscosity so that it can be easily pumped to the mixing head. If a homogeneous activator solution is not employed, the materials would have to be pumped separately to the mixing head. This results in foam cells that are not as fine or as uniform as when an activator solution is used. N-butylmorpholine is an example of an amine catalyst which does not give a homogeneous activator solution.
U.S. Pat. No. 4,326,042 describes a three-part catalyst system comprising N-methoxypropylmorpholine, N-butylmorpholine and N,N'dimethylpiperazine which gives a homogeneous activator solution. However, it would be desirable if the total amount of catalyst could be reduced, especially the N-methoxypropylmorpholine component which is difficult to make.
It would therefore be a substantial advance in the art if an amine catalyst or catalyst system were discovered which would overcome the disadvantages of the prior art.